Differential release paper



March 31, 1970 E. c. AYRES 3,503,782

DIFFERENTIAL RELEASE PAPER Filed May 29, 1967 2 Sheets-Sheet J INVENTOR.

E C. AY RE 5 ymififi March 31, 1970 E. c. AYRES 3,503,782

DIFFERENTIAL RELEASE PAPER Filed May 29, 1967 2 Sheets-Sheet 2 INVENTOR.E.C. AYRES A TTORNEYS United States Patent 6,503,782 DIFFERENTIALRELEASE PAPER Elwyn C. Ayres, Bartlesville, Okla., assignor to PhillipsPetroleum Company, a corporation of Delaware Continuation-impart ofapplication Ser. No. 602,841,

Dec. 19, 1966. This application May 29, 1967, Ser.

Int. Cl. D2111 1/10; B44d 1/14 U.S. Cl. 11745 13 Claims ABSTRACT OF THEDISCLOSURE A differential release paper having an initial coating of afirst release agent and a coating of second release agent applied over aportion of the initial coat; the release agents having different releasecharacteristics.

This is a continuation-in-part of my copending application, Ser. No.602,841, filed Dec. 19, 1966, now abandoned.

This invention relates to a method for applying a release agent to thesurface of a paper substrate. In another aspect, it relates to animproved differential release paper.

Differential release papers will be defined in this application as thosepapers wherein the surfaces have nonsimilar release characteristics.Applying a release agent to part of an area refers to placing a releaseagent on only a portion of the surface, either in a particular patternor not. A release agent will be defined as a material that promotes therelease of an adhesive bonded thereto so as to not damage the adhesivequalities.

Prior art provides for altering the release strength of a surface coatedwith release agents by altering the characteristics of the release agentitself. Stated another way, the prior art teaches the application of therelease agent over the entire surface and selection of a particularrelease agent to achieve a given release strength.

This invention provides for an improvement over the prior art in thatthis invention provides for the alteration of release strength bycovering with a release agent only a part of a surface that previouslyhas been completely covered with a different release agent. In otherWords, rather than selecting a release agent that corresponds to a givenrelease strength, it is now possible to produce a surface of desiredrelease strength by applying a release agent of greater release strengththan desired only to a part of a surface that has been first completelycoated with another release agent.

In one embodiment, the invention was used to create a differentialrelease paper by coating both sides of a paper completely with a firstrelease agent and then coating only a part of one side with a secondrelease agent; the release agents having different releasecharacteristics. Other embodiments of this invention include completelycoating one side and then applying a release agent over only a part ofthe same side, and also completely coating both sides with a firstrelease agent and applying a second release agent to only a part of bothsides.

The functioning of a release agent will now be described. According tothis invention, a release agent is applied to paper substrate. If therewere no release agent applied to the paper, the paper would not pullfree when bonded to an adhesive. If, however, a release agent has beenfirst applied to the paper and then the release agent bonded to theadhesive, the paper and release agent will pull free from the adhesivewithout damaging the adhesive. Stated another way, the release agentprotects the adhesive from coming in contact with the paper, and

3,503,782 Patented Mar. 31, 1970 ice thus prevents the paper fromdamaging the adhesive when pulled away.

In certain situations, it is desirable to produce a substrate that willrelease from one side at a greater or lesser strength than the otherside. This can be accomplished by selecting release agents of differentrelease strength for each side. According to this invention, however, adifferential release strength phenomenon is effected by coating bothsides with a release agent of equal release strength and then applying asecond release agent of greater or lesser release strength to only aportion of one side. Thus, the release qualities of the side to whichthe second release agent is applied result from a combination of therelease powers of both the first and second release agents. If thesecond release agent has a greater release strength than the firstrelease agent, then the release strength of the combination of the firstand second release agents is greater than the first release agent alone.Stated another way, the side coated in its entirety with the firstrelease agent and then partially coated with the second release agentreleases at greater strength than the side coated only with the firstrelease agent. Thus, a differential release phenomenon has beeneffected. If the second release agent has a lesser release strength thanthe first agent, the side partially coated with the second release agenthas a composite release strength less than the other side.

The invention resides in applying a release agent to only a part of asurface that has been first coated in its entirety with a release agentwhich has an inherent degree of release ability. In a preferredembodiment, the second coating is applied in the form of a pattern. Itis, however, fully within the scope of this invention to apply thesecond coating of release agent in any manner that results in onlypartial coverage of the surafce.

Accordingly, it is an object of the invention to provide an improveddifferential release paper.

Another object of this invention is to provide an alteration in releasestrength by coating with a release agent only a part of a surface thathas been previously covered completely 'with a release agent.

Another object of this invention is to provide a differential releasepaper by first coating both sides with a release agent and then coatingonly a part of one side with a release agent.

Other objects, advantages, and features of this invention will bereadily apparent to those skilled in the art from the followingdescription, drawing, and appended claims.

With reference to FIGURE 1, there is indicated a cross-sectional view ofone embodiment of this invention. With reference to FIGURE 2, there isindicated a plan view of the same embodiment of the invention.

With more particular reference to FIGURE 1, there is indicated a papersubstrate 10. Specifically, paper coated on both sides with polyolefinsis entirely satisfactory. Some polyolefins, such as polyethylene, haveinherent degree of release ability. Paper is used in the practice of theinvention because of the wide variety of applications in which it can beemployed. It should be understood that the invention is not limited toany particular type of paper. The invention is applicable to any paperhaving sufficient tensile strength to be handled in conventional papercoating :and treating apparatus. Thus, the invention is applicable toall types and weights of paper ranging from glassine to heavypaperboard, e.g., having weights in the range of from 25 to pounds perream.

With further reference to FIGURE 1, there is indicated a release agentcoating 11 applied to the entirety of a first side. This coating cancomprise a wide variety of release agents. Those materials comprisingorgano- S!iS il I The compositions used in the practice of theinventionare preferably, but not necessarily, high molecular weightpolymers and copolymers having molecular weights in the range of 5000 to250,000. They should not have obtained such a degree of polymerizationor condensation that they are no longer soluble in common hydrocanbonsolvents, such as xylene; toluene, methyl ethyl ketone, and carbontetrachloride. In general, any organic solvent having a boiling pointequal to or less than that of xylene can be used in the compositionsused in the practice of the invention. The solvent merely serves as aconvenient vehicle or carrier for uniform application to the substrate.Thus, higher boiling point solvents can be used but require so much timefor their removal that their use is not commercially economical. Variousorganopolysiloxanes are commercially available in organic solvents, invarious percent solids concentration.

Generally speaking, organopolysiloxanes which can be used in thepractice of the invention include those polymers wherein the recurringstructural unit is those polymers wherein the recurring structural unitis i those polymers wherein the recurring structural unit is l andcopolyrners wherein the recurring structural units are (2) and (3) asabove. In the above recurring structural units each R can be anysuitable monovalent hydrocarbon radical such as aklyl, cycloalkyl, aryl,alkaryl, and aralkyl. Preferably, each R is selected from the groupconsisting of alkyl radicals containing from 1 to 6 carbon atoms, andphenyl. Compositions wherein each R is methly, ethyl, phenyl arepresently more preferred.

Another type of structural unit which may be found in theabove-described organopolysiloxanes in small amounts is wherein R is asdefined above. This structural unit is found as a terminal unit in apolymer chain because the R groups are not capable of further condensingor crosslinking.

Examination of the above structural units (2), (3), and (4) shows thatin a polymer consisting essentially of recurring units of (2) or (4) theR/Si ratio (numerical ratio of the number of R groups to the number ofSi atoms) will approach 2 when one does not consider the terminal units(5). It is obvious that in the high molecular weight polymers (about5,000 to about 250,000 molecular weight) it is perfectly proper to notconsider the few terminal groups which will be present. Similarly, in apolymer consisting essentially of recurring units of (3), the R/Si ratiowill approach 1. It is also within the scope of the invention to mix anduse physical mixtures of said polymers consisting essentially of saidrecurring structural units (2), (3), and (4), and wherein the R/Si ratiois between about 1 and about 2. Thus, broadly speaking, theorganopolysiloxanes which can be used in the practice of the inventionare those having a R/ Si ratio within the range of from about 1 to about2.

However, the presently more preferred organopolysiloxanes for use in thepractice of the invention are said copolyrners consisting essentially ofrecurring structural units like (2) and (3) above, i.e.,

wherein each R is as defined above. Such copolyrners can be preparedaccording to methods known to the art. For example, by hydrolyzing amixture of desired amounts of dimethyldichlorosilane monomer andmethylhydrogendi chlorosilane comonomer,

and

where x and y are integers which represent the amount in mols of therespective monomers used in said mixture and which determine the R/ Siratio in the copolymer. A small amount of trimethylchlorosilane, (CHClSi, is added to supply the terminal (CH Si end groups. Other methodsof preparing said copolymers are known to the art. For example, saidcopolyrners can be formed by preparing cyclic tetramers of each monomerin dilute solution in suitable solvent and then causing rearrangement ofthe cyclic compounds in the absence of solvent.

Preferred copolymers are those where the R/Si ratio is within the rangeof from about 1.75 to less than 2, more preferably about 1.9 to lessthan 2, still more preferably about 1.95 to about 1.99. When neglectingthe (CH Siterminal groups as discussed above, the relationship between xand y and the R/Si ratio can be illustrated by the following tabulation,Table I.

It is obvious that the above relationships will not hold in lowmolecular weight copolyrners because of the extra CH group in theterminal group. However, in the high molecular weight copolyrners usedin the practice of the invention (about 5,000 to about 250,000 M.W.) theeffect of said terminal groups can be disregarded.

The presently most preferred organopolysiloxane for use in the practiceof the invention is a copolymer prepared, for example, by hydrolyzing amixture such as (7) above wherein x is about and y is about 5 to give aCHg/Sl ratio of about 1.95.

Since in the above illustrated monomers (7) each molecule ofdimethyldichlorosilane monomer furnishes one structural unit (2) whereinR is CH and each molecule of methylhydrogendichlorosilane monomerfurnishes one structural unit 3) wherein R is CH the preferredcopolymers of the invention can be described as consisting essentiallyof the recurring structural units (2) and where R is as defined above,and x and y as are defined above and denote the relative numbers of saidstructural units in the copolymer and determine the R/Si ratio. Forexample, referring to Table I, when x=95 and y=5, the copolymer willcontain 95 of the structural units (2) for each 5 of the structuralunits (3) and the R/Si ratio will be 1.95 when disregarding the terminalgroups. Since there will always be some of the structural unit (3)present in the copolymer, the R/ Si ratio will approach 2 for decreasingvalues of y which are less than 1. However, when disregarding theterminal (R) Si groups as discussed above, said ratio will always beless than 2.

The other above-described organopolysiloxanes can be prepared in anumber of ways, all known in the art. For example, the preparation ofmethyl polysiloxane, also known as methyl silicone resins, is describedin US. Patent 2,258,218. The preparation of ethyl polysiloxane resins,also known as ethyl silicone resins, is described in U.S. Patent2,258,220. US. Patent 2,258,222 described still other types of siliconeresins wherein one methyl radical in the structural units describedabove is replaced with an aryl group, such as a phenyl group. Othermethods of preparing said organopolysiloxanes are described in US.Patent 2,494,920.

Filler materials in finely divided form, can be added toorganopolysiloxanes to control the rheological properties and releasecharacteristics of the agent. The filler materials can be eitherinorganic or organic, are chemically inert with respect to theorganopolysiloxanes and substantially insoluble in the solvent used asthe vehicle in applying the release agent.

Examples of inorganic fillers which can be employed include calciumcarbonate, titanium dioxide, silica, alumina, mica, calcium silicate,zinc oxide, iron oxide and other polyvalent metal oxides. Examples oforganic filler material which can be used include poly (vinyl chloride);polyesters, such as Mylar; polyamides, such as nylon; polycarbonates,such as Lexan; and other thermoplastic or thermosetting polymers orresins.

The particle size of the filler material is not critical over a Widerange so long as the material is in a finely divided state, for example,materials having a particle size in the range of 0.1 to 250 microns, orgreater, can be employed. It is important that the filler material bethoroughly mixed into a uniform suspension in the organopolysiloxanecoating composition. The fillers are usually added in a filler tosilicone weight ratio within the range of from 0.25:1 to 3:1, based onthe silicone solids in the organopolysiloxane coating composition.

The above-described organopolysiloxanes in solution, and either filledor unfilled as described herein, are applied to the substrate surfacesin amounts, on a dry basis, within the range of from 0.03 to 0.4,preferably 0.06 to 0.25, pound per ream. Preferably, saidorganopolysiloxane is applied in two thin coats. However, it is withinthe scope of the invention to make the application in one coat. Theamount and type of organopolysiloxane in each said coat on the same sideor on opposite sides of the substrate can be the same or different.

The composition of the filled organopolysiloxane coating compositionswhich can be used in the practice of the invention can vary over a widerange, depending upon the properties desired. Usually the amounts of thecomponents of said composition will be within the following ranges, inweight per cent: polymeric silicone solids, from about 2 to aboutfiller, from 0.5 to about 30; and solvent, from about 60 to 97.5. Saidsolvent can be any of the solvents normally used for preparing solutionsof organopolysiloxanes as set forth above. When the filler is one of theabove-described organic fillers, it is sometimes desirable that fromabout 4 to about 10 percent of said solvent be an aliphatic hydrocarboncontaining from 5 to 9 carbon atoms per molecule, or mixtures thereofsuch as light naphthas and gasolines, to control the solubility of saidfiller in the overall solvent. Parafiinic and isoparafiinic hydrocarbonsare preferred.

Prior to application of the organopolysiloxane coating composition, asmall amount of a suitable catalyst or curing agent is added thereto.Suitable catalysts for this purpose include dibutyl tin di-Z-ethylhexanoate, dibutyl tin dilaurate, dibutyl tin diacetate, tributyl tinacetate, diethylene triamine, triethylene tetramine, various lead saltssuch as lead naphthenate and lead octoate, zinc octoate, zinc stearate,iron octoate, various organic peroxides such as benzoyl peroxide, andothers. The amount of said curing agents or catalysts used is notcritical and can be varied widely depending upon the curing temperature,the particular catalyst used, desired curing time, the particularsilicone polymer, etc. Usually, the amount used will be from 1 to 10weight percent of the silicone polymer.

Curing of the organopolysiloxane coating material can take place at roomtemperature depending upon the particular silicone material used and theparticular curing agent or catalyst used in conjunction with thesilicone material. However, for practical continuous operation the timerequired for curing at room temperature is too long. Most curing agentsare capable of promoting relatively rapid curing at moderately elevatedtemperatures. This temperature at which relatively rapid curing takesplace is sometimes referred to as the curing initiating temperature eventhough curing will take place at room temperature. For the preferredorganopolysiloxanes described herein, this temperature is in the rangeof to 250 F. Once curing has been initiated and maintained at anelevated temperature for a short period of time, the curing can beallowed to proceed by aging at reduced temperature, for example roomtemperature, to obtain a substantially dry film.

With additional reference to FIGURE 1, there is indicated a releaseagent coating 12 applied to an entirety of a second side of substrate10. All comments concerning release agent coating 11, applied to theentirety of a first side, are equally applicable to release agentcoating 12, applied to the entirety of a second side. With furtherreference to FIGURE 1, there is indicated release agent coating 13applied in a pattern. In this specific embodiment of the invention thepattern consists of a series of lines. It is fully within the scope ofmy invention, however, to alter the pattern to include a patterncomposed of any geometrical unit, such as dots, squares, triangles,rectangles, and the like. It is also within the scope of this inventionto apply release agent coating 13 in a nonpattern formation, such asrandom placement of the agent. It is then readily obvious that anyapplication of release agent is satisfactory as long as only a part ofthe surface is covered.

FIGURE 3 and FIGURE 4 depict a substrate 20 having a polyolefin coating21 on both sides. The polyolefin coating 21 is coated with a firstrelease agent 22. The top coating of release agent 22 is overcoated witha dot pattern of a second release agent 23 in this embodiment of thisinvention.

EXAMPLE In one specific embodiment of this invention, a dilferentialrelease substrate was produced and tested. Specifically, a substratecomprising paper with a .85 mil-thick polyethylene layer on both sideswas coated, by use of a gravure roll, with a first unfilledorganopolysiloxane release agent on both sides and cured. One side wasthen overcoated with a dot pattern of a second silicone release agent ofan organopolysiloxane with a resin filler and dibutyl tin di-2-ethylhexonate as a curing agent and cured. This embodiment is illustrated inFIGURE 3 and FIG- URE 4. This second release agent had greater releasecharacteristics than the release agent used for the initial coating.

A first sample was prepared with only the coating of first release agentas a control. A second sample, similar to the first, was prepared and anovercoat of the second release agent was applied in a dot pattern, thedots being about of an inch apart. A third sample, similar to the first,was prepared and an overcoat of the second release agent was applied indot pattern, the spacing between clots being less than that of thesecond samples. The samples were tested by stripping Johnson & JohnsonRed Cross Waterproof Adhesive Tape from the sample surface at aconstant-speed pull of 12 inches per minute. A Keil testing machine wasemployed in the testing. The average release values for the threesamples are given below:

This data indicates the higher release characteristics obtained from thepattern coating. Also, comparison of the release values for samples 2and 3 shows the effect of the pattern density or dot frequency on therelease characteristics.

In this embodiment the second release agent possessed greater releasecharacteristics than the first release agent. This resulted in theincreased release characteristics shown in the data. If the secondrelease agent had possessed a lower release characteristic than thefirst coating the result would have been a reduced releasecharacteristic.

Reasonable modification and variation are Within the scope of theinvention which set forth a novel differential release paper. I

What is claimed is:

1. A method of producing a surface having a desired release strengthcomprising the steps of uniformly applying a first release agent coatingto one surface of a paper substrate so as to entirely cover said onesurface; and applying a second release agent coating of a differentrelease agent to only a part of said one surface.

2. The method of claim 1 wherein said second release agent coating isapplied in the form of a pattern,

3. The method of claim 2 wherein the part of said surface to which thesecond release agent is applied comprises a dot pattern.

4. The method of claim 1 wherein each said release agent comprises acured coating of an organopolysiloxane having an R/ Si ratio within therange of about 1 to about 2, where R is a monovalent hydrocarbonradical.

5. The method of claim 4 wherein said monovalent hydrocarbon radicalcomprises CH 6. The method of claim 1 wherein a third release agentcoating is applied to a second surface of said paper and the releasestrength of said third coating is different from the release strength ofthe combined coating on said one surface.

7. The method of claim 6 wherein said first and third release agentcoatings are of the same release agent.

8. An article of manufacture of differential release characteristicscomprising a paper substrate; a first release agent coating totallyapplied to a first side of said substrate to. form a first surface; asecond release agent coating totally applied to a second side of saidsubstrate to form a second surface; and a third release agent coatingapplied to a part of said first surface.

9. The article of manufacture of claim 8 wherein said paper substratecomprises a paper coated on both sides with polyethylene; and whereinthe part of the surface to which the third release agent is appliedcomprises a dot pattern.

10. The article of manufacture of claim 8 wherein said third releaseagent coating is applied in the form of a pattern.

11. The article of manufacture of claim 8 wherein said first and thirdcoatings are of the same release agent.

12. The article of manufacture of claim 8 wherein each said releaseagent comprises a cured coating of an organopolysiloxane having an R/Siratio Within the range of about 1 to about 2, Where R is a monovalenthydrocarbon radical.

13. The article of manufacture of claim 8 wherein said monovalenthydrocarbon radical comprises CH References Cited UNITED STATES PATENTS2,816,655 12/1966 Crozier et al 117-685 ALFRED L. LEAVITI, PrimaryExaminer M. F. ESPOSITO, Assistant Examiner U.S. Cl. X.R. 11776; 156-289UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION March 31, 1970Patent No. 3 503 732 Dated Elwyn C. Ayres Inventor(s) It is certifiedthat error appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Column 8 line 30, delete the numeral "8" and insert therefor the numerall2 SIGNED AND SEALED AUG 1 11970 EdwndH-Fletdxmln H commissioner ofPatents 5 FORM PO-1050 (IO-69) USCOMMDC QO3TU PGP 9 US GOVERNMENYPRINTHIG OFFICE: III. 0-Sil-8ll

